Grain legume seed filling in relation to nitrogen acquisition: A review and prospects with particular reference to pea

Seed filling depends not only on the instantaneous supply of C and N, but a lso on their remobilisation from vegetative organs. C supply during seed fi lling depends mostly on current photosynthesis, but N assimilation and N-2 fixation decline during seed filling, with newly acquired N generally insuf ficient for the high seed demand. As seeds are strong sinks for mobilised n utrients, seed growth becomes metabolically closely associated with N remob ilisation. N remobilisation from vegetative tissues to filling seeds intera cts with photosynthesis since it induces senescence, which reduces the seed filling period. Hence improved grain legume seed filling requires either r educed dependency on N remobilisation or enhanced N supply. This latter mig ht be obtained either by prolonging the activity of symbiotic fixation, inc reasing the potential for root assimilation of soil mineral N or optimising complementarity between both N acquisition pathways, which does not affect the quantity and the quality of the seed reserves.